Predominantly in the field of consumer electronics, but also, for example, in the design of motor vehicles and other devices, device surfaces are often provided with light-emitting decorative elements. Such decorative elements frequently represent a logo of the device manufacturer or decorate contours of the object to which they are attached. Both for aesthetic reasons and for the purpose of energy saving, which is a frequent requirement in particular in the case of mobile devices with a battery-based power supply, the illumination intensity of such decorative elements is generally chosen to be relatively weak. In addition, illumination often takes place only when the device is in an active operating state, which serves both to save energy in the non-operating state and to make an active state of the device recognisable.
Owing to the often weak or non-existent active illumination of the described decorative elements, it is desirable for such elements to appear visually attractive even when their own illumination is switched off and in strong ambient light. To that end, they can be provided with a partially reflective surface, which reflects a large part of the incident ambient light in the manner of a mirror but at the same time is partially transparent to the light of a light source arranged beneath the surface. The appearance of such decorative elements thus varies, in dependence on the switching status of their light source and the ambient light conditions, between a luminous and a reflecting surface.
The use of partially reflective surfaces requires a compromise between, on the one hand, a satisfactory mirror effect for strong ambient light, which prevents the light source located beneath the surface from being visible, and, on the other hand, a sufficiently high transmissivity for the light emitted by that light source during operation. The necessary reflectivity for ambient light in most cases requires high absorption of the light emitted by the light source, which is undesirable in particular in view of the energy efficiency of illuminated decorative elements in mobile devices.
It has therefore been shown that decorative elements which avoid the above-mentioned disadvantages of low reflectivity or high absorption are desirable.